1. Field
Example embodiments relate to magnetic memories and methods of operating the magnetic memories, for example, spin transfer torque magnetic random access memories (STT-MRAMs) and methods of operating STT-MRAMs.
2. Description of the Related Art
Magnetic random access memories (MRAMs) are memory devices for storing data by using variations in resistance of a magnetic tunneling junction (MTJ) element of a memory cell. Resistance of a MTJ element varies according to a magnetization direction of a free layer. For example, when the magnetization direction of the free layer is the same as a magnetization direction of a fixed layer, the MTJ element has a relatively low resistance. When the magnetization direction of the free layer is opposite to the magnetization direction of the fixed layer, the MTJ element has a relatively high resistance. A case where the MTJ element has a relatively low resistance may correspond to data ‘0’, whereas a case in which the MTJ element has a relatively high resistance may correspond to data ‘1’. In order to read data stored in a memory cell of the MRAM, there is a need for a reference cell that is used as a reference (basis) of resistance.
An MRAM (hereinafter, referred to as a general MRAM) records data in a MTJ element using a digit line. In a general MRAM, a magnetization direction of a free layer is reversed using a magnetic field generated by the digit line spaced apart from the MTJ element by supplying a current (e.g., a write current) to the digit line. A read current is supplied between ends of the MTJ element. As such, in a general MRAM, the write current need not be considered in configuring the reference cell because paths of the read current and the write current are different from each other.
Unlike general MRAMS, STT-MRAMs do not use digit lines. In conventional STT-MRAMs, a reference cell circuit having a structure different from that of a general MRAM is required because the paths of the read current and the write current are the same.